Prolactin levels are determined in patients with pituitary dysfunction during dynamic provocative stimulation. The emphasis is on patients with prolactin secreting pituitary adenomas, pre and post surgical adenomectomy. Patients with hyperprolactinemia and hypopituitarism are also being studied under this protocol. The dynamic studies in the latter group is likely to help define the mechanism of hypopituitarism in these patients. The data documenting the usefulness of prolactin dynamic studies in predicting the long term benefit from transsphenoidal surgery in patients with prolactin secreting pituitary adenomas were published in 1986. Prolactin levels are often elevated in patients with functioning or non functioning adenomas associated with hypopituitarism. Our study has demonstrated that the degree of prolactin level elevation under these situations, correlate with the potential for recovery of pituitary function after decompressive surgery. We are in the process of comparing and contrasting data on the dynamics of prolactin secretion with that obtained from evaluating the pulsatile aspect of prolactin secretion in the same patients. The long term follow up of patients who had surgical resection of pituitary adenomas 10 to 25 years ago, is being assessed. We have a major advantage in following a relatively large number of these patients to allow us to do these long-term studies.